


A Killer Hypothesis

by zinke



Category: Castle
Genre: Case Fic, Ensemble Cast, Family, Friendship, Gen, Gift Fic, Humor, Suspense, Unresolved Sexual Tension
Language: English
Status: Completed
Published: 2012-03-31
Updated: 2012-03-31
Packaged: 2017-11-02 19:35:11
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 4
Words: 7,472
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/372606
Author URL: https://archiveofourown.org/users/zinke/pseuds/zinke
Summary: <blockquote class="userstuff">
              <p>"Death by pillow fight? C’mon!" Castle exclaims. "Tell me you’re not titillated."</p>
            </blockquote>





	1. Part One

**Author's Note:**

> Several months ago, reema-patel won LJ's safeword_apples Mini-Hiatus Pop Quiz contest, the spoils of which was a 500 word fic from me based on a prompt of her choosing. The prompt she gave me was: _pillow fight_ , which it turns out was a pretty awesome prompt because my little 500 word vignette has since turned into a full-on case file. Oops? In any case, I thank her for her patience; this story has been far too long in coming. 
> 
> Research information cited in this story is taken from the [National Alzheimer’s Association Research Center](http://www.alz.org/research/overview.asp) and [Science Daily](http://www.sciencedaily.com/releases/2011/12/111209105746.htm).
> 
> Thanks goes as always to my own personal adverb protection officer gabolange> and to girlunravelled who helped nurse me through the daunting plot-writing process.

* * * *

_The great tragedy of science: the slaying of a beautiful truth by an ugly fact.  
-Thomas Huxley_

* * * *

“Claudia?”

Dressed in running shorts and a tight-fitting lettered jersey, the young brunette sweeps the hair from her eyes as she reaches the top of the stairs and peers down the hallway. “Clau-d-ia!” she sing songs in between swigs from the super-sized travel mug in her hand. “Where are you?”

Bobbing her head in time to the heavy, thumping base of Lady Gaga’s ‘Edge of Glory’, she makes her way past the row of identical looking doors, singing along under her breath as she goes. Stumbling to a stop, she leans against the jamb and knocks impatiently on the heavy oak door.

“Claudia, come on! Dana’s already dealt the next hand. Everyone’s waiting.”

She waits a few seconds before trying the knob. It turns easily in her hand and, after a moment’s hesitation, she steps inside.

And screams. 

* * * *

“Tell me Esposito wasn’t lying.” 

Beckett looks up from the body to find Castle practically tripping over himself in his haste to duck under the yellow tape marking the perimeter of the crime scene. She watches his eyes dance from Javier, who is interviewing a young woman wearing a Greek-lettered jersey and little else, to the body lying on the dorm room floor in a drift of grey feathers, a ripped pillowcase still wound tight around her throat.

“Castle, would you at least _try_ not to look so excited? This is a crime scene.”

“Death by pillow fight? C’mon!” Castle exclaims. “Tell me you’re not titillated.”

Beckett shoots him an exasperated look. “Aren’t you getting a little old for these co-ed fantasies of yours?”

Castle eyes her as if she’s spontaneously grown a second head. “No.” 

“Sorry to disappoint you Castle,” Lanie interrupts, “but it wasn’t that kind of pillow fight.” She points to wounds on the girl’s arms as both Beckett and Castle crouch down to get a closer look. “She tried to fight him off. If I had to guess, the killer grabbed the pillowcase from the pile of laundry at the foot of the bed.”

“Which means this wasn’t a premeditated attack. Our killer was forced to get creative.” Beckett rises as Ryan comes up beside her. “Anything?”

Ryan shakes his head. “Apparently the music was on pretty loud downstairs. The last time anyone remembers seeing our vic was around eleven o’clock.” 

“Who found her?”

Ryan nods toward the shaken looking brunette being interviewed by Esposito. “Mandy Sheppard. Vice President of the Zeta Beta chapter of Gamma Alpha Lambda. She came looking for her when she didn’t show up for the next round of Five Card Yak.”

“And our victim was…?” 

“Claudia Santos. Chapter President.”

“Ahhh,” Castle breathes as he straightens from his crouch. “Locked in a desperate struggle for power, a jealous Mandy Shepherd decides to forgo democratic process and take matters into her own hands.”

“This isn’t a David Baldacci novel, Castle.” 

“It’s a _sorority_. I promise you, these girls could put even the filthiest of political mudslingers to shame.” 

“Waging a smear campaign is one thing. But are you honestly telling me you think that she,” Beckett says, waving a hand in Mandy’s direction, “is capable of strangling a person to death?”

Together they watch as the girl in question lets out an ear-piercing sob and collapses against a bewildered looking Esposito. He awkwardly puts an arm around her shoulder and shoots a pleading look in their direction. 

“It’s a theory,” Castle concedes with a shrug.

“Not a very good one,” Lanie chimes in as she stands and pulls off her gloves and gives the techs the go-ahead to prepare the body for transport. “Whoever did this to her was strong. So unless one of these girls happens to play defensive end for the football team…”

Beckett nods. “Thanks, Lanie.”

“I’ll give you a call as soon as I know more,” she says to Beckett before turning to follow the gurney out of the room.

“So…probably not one of her sorority sisters,” Castle says, sounding disappointed. 

Beckett frowns. “Probably not.”

“We’re still working our way through the witness interviews,” Ryan says as Castle wanders off to make a slow circuit of the tiny room.”Maybe one of the other girls will have heard or seen something.”

Castle stops to consider the array of snapshots taped to the full length mirror on the closet door. “What were they all doing here, anyway?”

Ryan gives Castle a strange look. “They live here.”

“What I mean is, it’s after midnight on a Saturday. Shouldn’t these girls be out getting down or hooking up or whatever it is college kids do these days?”

Esposito casts a glance back at the still-teary girl being led from the room. “According to Miss Shepherd the Gammas were holding an overnight members only lock-in. No one in or out after nine o’clock.” 

Castle’s expression brightens. “Which means it _was_ one of the sorority sisters—“

“—Or,” Beckett interrupts, “the Gammas had an uninvited guest earlier tonight.” 

Ryan has no trouble interpreting the meaningful look Beckett sends towards the room’s open window. “I’ll see if we can get security camera footage from University Police.”

“I’ll take a few uniforms, have a look outside,” Esposito adds before turning to follow his partner out of the room. 

“Thanks, guys.” Kate watches them go before turning to look for Castle. She finds him standing on the far side of the room, perusing a collection of liquor bottles on top of the room’s mini fridge. “Castle? You find something?”

Shaking his head, he picks up a half-empty bottle of Stolichnaya and sighs wistfully. “Just remembering what it would be like to be young again and indulging my many vices on my mother’s dime.”

“You can’t be serious.”

“Wouldn’t you want to go back?” Castle looks over the photos in the room, all filled with smiling faces at football games or crowded parties, laughing over red Solo cups. “Do all this again?” Castle realizes just what he’s asked her a moment too late. “Of course you wouldn’t. I’m sorry.” 

“Its okay, Castle,” she assures him as together they head out the door and down the hallway to the stairs. “Believe it or not, I have a lot of good memories from college.” 

“Really?”

“Really. And before you ask; none of them even remotely resemble a scene out of ‘Porky’s’.”

“I wasn’t—”

“You were.”

“Okay, yes, I was. But you can’t honestly tell me that all you did in college was attend classes and go to the library.” 

Beckett gives him a coy smile. “You’d be surprised how much fun you can have in the rear stacks of Bobst Library.”

Castle stops short on the landing, his jaw hanging slightly as a smirking Beckett continues down the stairs without him. 

* * * *

“So, what do we know?”

Beckett accepts the steaming mug of coffee Castle offers her without taking her eyes from the murder board. “Aside from the fact that Claudia Santos was a model student? Not much.”

Sitting next to Beckett on the edge of the desk, he studies the various pictures and notations laid out before them. “Pre-med, 3.8 GPA. Rhodes Scholar finalist. Research assistant in the University’s bio lab, academic tutor, member of the intramural volleyball team, co-chair of the school’s volunteer services committee. Was there any campus activity Claudia _wasn’t_ involved in?”

Kate acknowledges the point with a nod. “Her achievements certainly put jealousy into play as a possible motive.” 

“I feel a ‘but’ coming on.”

“But,” Beckett says, raising her mug to her lips in an effort to hide her amusement, “I’m going to keep an open mind until we know more. And so should you.” 

“Don’t I always?”

Beckett shoots him a disbelieving look just as Ryan calls out, “Hey Beckett, you need to take a look at this.”

“The security camera footage?” she asks as she pushes to her feet and crosses the bullpen to his desk.

Ryan nods. “We got a hit on one of the cameras facing the west side of the building at around ten-thirty.”

“Oooh. A party crasher,” Castle breathes as he peers over Beckett’s shoulder at the grainy video playing on the computer screen. “Is he climbing the side of the building?”

Ryan nods as the person in question hoists himself up and through an open second-story window. 

“That? Is _not_ an easy thing to do.” Castle adopts an affectedly innocent look. “Not that I have any experience at all with that sort of thing.”

“Were you able to get an ID?” Beckett asks Ryan.

“University police are working on it now. If we’re lucky, they’ll be able to match our guy to someone in the school’s student database.”

“Not someone,” Esposito calls out as he rounds the corner and hands Beckett a folder. “Daniel McCall.”

“McCall…” Castle’s eyes widen in recognition. “Three-time all-conference MVP, winner of the Biletnikoff Award, Danny ‘Sticky Fingers’ McCall?”

Esposito nods. “That’s the one.”

Castle whistles softly. “Lou Holtz has him picked to go top ten in next year’s draft.” 

“Yeah, well, it looks like Mr. McCall’s scholastic record isn’t quite so impressive. He’s on academic probation. One more misstep and he’ll be benched for the rest of the season.” Beckett turns to the next page in his file. As she reads, her lips curl into a cat-who-got-the-canary grin. “And guess who his biology tutor is?”

“Failing class and enraged at the thought of losing millions of dollars in lucrative aftershave endorsement contracts, Danny McCall takes his anger out on the one person who was supposed to save him from his own stupidity.” Castle pauses and takes in the others’ expressions. “Too much?”

Beckett shakes her head. “Let’s bring him in.” 

 

*end part one*


	2. Part Two

**Summary for the Chapter:**

> "You do understand you’re under suspicion for murder?" Castle asks. "In the grand scheme of things, losing a scholarship should be the absolute least of your worries."

**Notes for the Chapter:**

> Several months ago, pillow fight, which it turns out was a pretty awesome prompt because my little 500 word vignette has since turned into a full-on case file. Oops? In any case, I thank her for her patience; this story has been far too long in coming. 
> 
> Research information cited in this story is taken from the [National Alzheimer’s Association Research Center](http://www.alz.org/research/overview.asp) and [Science Daily](http://www.sciencedaily.com/releases/2011/12/111209105746.htm).
> 
> Thanks goes as always to my own personal adverb protection officer gabolange and to girlunravelled who helped nurse me through the daunting plot-writing process.

Crossing her arms, Beckett leans back in the interrogation room chair and sizes up her less-than-cooperative suspect. On the far side of the table, Daniel McCall is doing his best to look nonchalant – and failing miserably.

She watches him pick at a crack in the table’s veneer, letting him sweat for a few seconds longer. “Daniel.” When he doesn’t respond, Kate reaches across the tabletop to still his hand. “Danny. I need you to tell me what happened.”

“Nothing happened, I told you.”

“Something _did_ happen. A woman was murdered – a woman you knew.” Castle says. “And you were there.”

“No!” Danny licks his lips. “I wasn’t. I swear.”

“Yes, you were.” Beckett pushes a still taken from the security video across the tabletop. “You just didn’t want anyone to know.” 

Castle pins McCall with a steely gaze. “Why is that, exactly?”

“It’s not—I didn’t—” The young man visibly deflates. “I’m on a scholarship,” he says, his gaze flicking between Castle and Beckett. “I lose that, I spend the rest of my life pumping gas at the local Lukoil.”

“You do understand you’re under suspicion for murder?” Castle asks. “In the grand scheme of things, losing a scholarship should be the absolute least of your worries.” 

“I didn’t kill Claudia!”

Beckett jabs a finger at the timestamp in the corner of the photograph. “Then tell me why we have security camera footage that clearly shows you sneaking into the Gamma house through Claudia’s open window less than an hour before she was found dead in her room?” 

“I wanted to see my girlfriend,” McCall blurts, his face flushing at the admission. 

“Your girlfriend?” Beckett prompts.

“Pixley Jones.” 

“Seriously?” Castle asks, his tone a mixture of disbelief and unabashed amusement.

Beckett sends a warning glance in Castle’s direction. “If you were there to see Pixley, then why did you climb in though Claudia’s window?”

“Because it was open,” McCall replies. “As soon as I was inside I called Pixley and told her to meet me in her room. She and I were…kind of busy after that.”

Beckett and Castle exchange a glance as McCall continues, “As soon as I heard Mandy scream I high-tailed it out of there before someone could see me.”

“And how exactly did you accomplish that?”

“I used the emergency exit,” he replies as if it were obvious. “No one ever goes in or out that way.”

“And you didn’t set off an alarm when you opened the door?”

Danny shrugs. “Must’ve been broken.” 

“Or intentionally disabled.” Castle shifts closer to Beckett and murmurs, “You know, if Danny Boy here is telling the truth that door could be how our killer got inside.” 

Beckett considers the idea a moment before returning her attention to their suspect. “Did you see anyone else when you left the Gamma house?” 

McCall shakes his head. “All I wanted to do was get my ass back to the library before Coach found out I was gone. He’d bench me if he heard I was…you know instead of studying for my stats exam.”

“Okay. So let’s say for the sake of argument that you didn’t kill Claudia. Did she say anything to you in the days leading up to her murder? Act differently or do anything out of the ordinary?”

“She did cancel a few of our tutoring sessions last week because she was working late in the biology lab.”

“Do you know what she was working on?”

Danny shakes his head. “Whatever it was, it must’ve been big.”

“Why do you say that?”

“She had that look in her eyes, you know?” 

Castle and Beckett shake their heads. 

"Listen; football is my life; science was Claudia’s. And the way she’d been acting the past couple weeks? You’d have thought the championship title was on the line and she’d just fumbled the ball.”

* * * *

Castle is sitting in his customary spot by her desk, slouched in his chair and tossing a wadded up ball of paper into the air when Beckett gets back from holding. “McCall’s story checks out,” she says as he sends it spinning into the air.

The paper drops to the ground, forgotten. “Raging hormones as an alibi? Really?”

“Really. Phones records confirm the call to his girlfriend a few minutes after the video shows him climbing through Claudia’s window. And Pixley—” Beckett narrows her eyes as Castle snickers, “corroborated his story that they were together in her room at the time of the murder.”

“If he didn’t do it, and all of the other Gammas alibied one another out—”

“Then we need to look outside the sorority house for our suspect.” Beckett sighs and sinks into her chair. “Hey Ryan? Do we have anything from CSU yet?”

“Uhh…” Ryan rifles through the stack of files on his desk until he finds the one he’s looking for. “Yeah; report came up while you were in interrogation. The only fingerprints they found on the fire exit door were McCall’s.”

Caste’s brow furrows. “That’s weird.” 

“How so?” Beckett asks.

“Manhattan University has over five-thousand students,” he explains. “There are probably just as many reasons why someone might’ve touched or tried to use that door since the last time anyone on the maintenance staff bothered to clean it.” 

Beckett nods in understanding. “Which means it was wiped clean shortly before Danny used it.”

“That would explain the two sets of footprints CSU found in the mud just outside the door,” Ryan adds.

“So somebody else _was_ there,” Castle says triumphantly as Beckett takes the CSU from Ryan and quickly scans its contents.

Beckett frowns and passes Castle the file. “Someone was there, yes. But we have no way of proving it was our killer. For all we know it was just another horny boyfriend who had the same bright idea as Danny.” 

“And had the foresight to cover his tracks on the way out the door?” Castle snorts. “You clearly don’t know much about horny teenage boys.” 

“What can I say, Castle?” She leans closer to breathe in his ear, “I happen to like my men a little more experienced.”

Smirking, she watches Castle splutter for a moment before turning to Ryan, her expression all business once again. “McCall said that Claudia had suddenly been spending a lot of time in the biology lab.”

“You think that might have something to do with why she was killed?”

“I think that, at the moment, it’s the only lead we’ve got.” Standing, Beckett reaches for the jacket hung across the back of her chair. “Looks like you’re getting your wish Castle; time to go back to school.”

“Not exactly what I had in mind,” he grouses, following her to the elevator. 

* * * * 

“Thank you for seeing us on such short notice, Professor.” 

Dr. Jeremy Tripp coughs and pulls a handkerchief from his pocket and gives Beckett a weak smile. “Under the circumstances, it’s the very least I could do. Claudia was one of my most gifted students.” 

Leading them into his office, Tripp dabs at his lips with the cloth before taking a long sip of water from the mug on his desk. “Please excuse me; I’m getting over a rather nasty cold.”

“It’s that time of year,” Beckett reassures as she looks around at the controlled chaos of Tripp’s office. Every available surface is covered in stack of books, journals, and loose papers, the bookshelves lining the far wall filled to bursting with more of the same. A line of stained coffee mugs stand sentinel along the window ledge beside a wilted, yellowing bamboo plant that has undoubtedly seen better days. 

Noticing her inspection, Tripp hurries to remove twin towers of paper from the pair of visitor’s chairs by his desk. “Please, sit.”

Beckett waits until the three of them are settled before asking, “Professor, I understand Claudia Santos has been assisting you in your research?”

Tripp tugs at the hem of his sweater vest and skims a hand over the length of his tie as he takes a seat. “Yes. For the last two years.”

“Her friends mentioned that she’d been spending a lot of extra time here over the past few weeks.”

“That’s right. We’d come to a critical point in my research, and I needed all hands on deck. Claudia was more than willing to put in the extra time.”

“And what exactly is it that you and your team have been working on?”

“The development of an antibody that can block beta-secretase and gamma-secretase enzymes, thereby preventing the fragmentation of Amyloid Beta from the amyloid precursor protein.” 

Off Castle’s blank look, Beckett explains, “They’re trying to find a treatment for Alzheimer’s disease.”

“Not treatment.” Tripp corrects, looking impressed. “A _cure_. By introducing an agent that interferes with the cleaving process, we can not only inhibit the development of the plaques that cause Alzheimer’s disease, but also repair existing damage to the neurons themselves.”

Castle’s eyes widen. “That’s impressive.” 

“It would change the face of aging as we currently know it,” Tripp agrees with a nod. 

“And Claudia wanted to be a part of that?” Beckett asks, pulling the focus of the interview back to the more immediate issue.

“She came to me personally and asked to be on the project. Her grandmother had been diagnosed a month or so earlier, and Claudia felt very strongly about becoming a part of the effort to combat the disease. I don’t usually take on undergraduate assistants but…” Tripp shrugs. “Claudia was different.” 

“How so?”

Tripp releases a raspy sigh and leans back in his chair. “She was bright, dedicated. Claudia had the mind of a true scientist. Her insights are no small part of the reason we’ve made so much progress over the past two years.” 

Castle leans forward. “How much progress is that, exactly?”

“Enough to be laying the groundwork to begin animal trials early next year. For the first time in my professional life, I can honestly say that I believe I will live to see the aspirations of my life’s work – a cure for one of the most insidious diseases on the planet – become a reality.” 

“That’s some pretty heady stuff for a research scientist.”

“’Heady’ doesn’t even begin to describe it, Mr. Castle.”

Beckett leans forward in her chair and makes a point of meeting the other man’s eyes. “I’m afraid we’re going to need to have a look at your lab.”

Tripp’s expression grows pale. “You can’t possibly think that my work had something to do with Claudia’s death?”

“We’re not sure,” Beckett gives the man a reassuring smile. “But I’m sure you can understand when I tell you that we need to explore every possibility before drawing our conclusions.” 

“Of course.” Tripp rises to his feet. “This way.” 

* * * *

It’s a short walk to the lab, a brightly lit expanse of white and chrome that stands as a stark contrast the earlier clutter of Tripp’s office. A cluster of workstations is situated at the center of the room, each one equipped with its own computer. Seated at one of the cubicles is a scruffy-faced man dressed in jeans and polo shirt. He looks up as Tripp swipes his keycard and opens the door, frowning slightly as he takes in the presence of the visitors. 

“Professor?” The younger man switches off his computer and rises to his feet. “How are you feeling?”

“Better, thank you. Simon, this is Detective Beckett and Mr. Castle. They’re investigating what happened to Claudia last night. Detective, this is Simon Moss, my post-graduate research assistant.” 

“I heard the news this morning,” Simon says, once handshakes have been exchanged. “It’s hard to believe.”

“Were you and Claudia close?” Beckett asks, casting a sideways glance at her partner as he leans in for a closer inspection of one of the empty workstations, remarkable only because of the lion’s mane of Post-It Notes ringing the edge of its computer monitor. 

“I supervised her here in the lab for over two years.” Simon’s eyes dart nervously between Beckett and Castle. “That’s a lot of hours spent hunched together over a microscope.” 

“And outside the lab?” 

“Frat parties and sorority mixers aren’t really my scene.” Simon frowns and points a finger at Castle. “What is he doing?”

“Is this Claudia’s computer?” Castle asks before Beckett can respond to the question.

Tripp nods. “Claudia had her own, unique way of working out a problem. She’d move those notes around the edge of the screen like puzzle pieces until something—” The professor stops short, giving Castle a strange look as the writer raises his phone and snaps a picture of the display, “—clicked.”

“Hey – is he allowed to do that?” Simon protests.

Beckett ignores the question. “We’re going to need to have a look at whatever is on Claudia’s computer.”

“But those files are confidential,” Simon protests.

“And they will stay that way,” Beckett assures. “But this is a murder investigation; my people are going to need access to all of Claudia’s files.” 

“I think what Simon is trying to say,” Tripp interjects, “is that, pocket protector stereotypes aside, the scientific community can be rather cutthroat, and if someone outside my group were to gain access to my research…”

“I understand.” Beckett flashes them both a reassuring smile. “And I assure you we will take every precaution to ensure that doesn’t happen.” 

“What precautions, exactly? Because—”

“Simon, please.” Tripp places a steadying hand on the younger man’s shoulder. “If it will help you find Claudia’s killer, naturally we will give you whatever access you need, Detective Beckett. But I must insist that your people do whatever is required here, on site, behind the University’s firewalls.”

“Of course,” Beckett says, her expression cool. “Just one last question before we let you both get back to your work: where were you last night between eleven and one?”

“At home,” Tripp responds. “I haven’t been feeling well and made a point of going to bed early.”

“And I was here, catching up on some data entry.”

“Alone?”

Simon nods.

“Thank you gentlemen,” Beckett says, straightening slightly as she gives them both a smile. “You’ve been very helpful.” 

* * * *

“I know that look,” Castle comments as they make their way outside and across the quad.

“What look?”

“The pursed lips, the furrowed brow, the death grip you’ve got on your cell phone.” He waits for her to self-consciously slip the device into her pocket before finishing, “You’ve got a hunch.”

Beckett gives him a sidelong glance. “Haven’t we had this conversation before?”

“I’m just saying: you’ve got a theory. And I think it’s time you shared with the class.”

“I’ll show you mine if you show me yours,” Beckett counters as she stops and turns to him with a smirk. 

“I don’t have one – yet.” Pulling his phone from his pocket, Castle brings up the picture of Claudia’s computer monitor he’d taken earlier. “But I’ll bet you a burger at Remy’s that the answer is here. Somewhere.” 

“In a bunch of Post-It Notes?”

He gives her a sour look. 

“All right, Castle. I’ll tell you what; as soon as you figure it out, call me.”

“I—what?”

“I’m assigning you to this particular line of investigation.”

“You can do that?”

“I just did.” 

Castle regards her with a mixture of surprise and anticipation. “Okay.” And with that he wanders off, his attention fixed on the picture on his phone’s screen.

“Hey!” she calls after him. “Aren’t you going to ask me about my hunch?”

“You think Simon did it,” Castle replies off-handedly.

“How did you—”

“He looks up from his phone with a smug grin.

“Never mind.”

He waits for her to catch up with him before resuming walking. “If it helps, I don’t know _why_ you suspect our graduate student of being a killer.”

“Because he’s hiding something.”

“’Something’ could be a lot of different things.”

“Well, for one, he wasn’t at the lab last night.”

“How—”

“The look on Tripp’s face when Simon gave us his alibi. The professor knew he was lying.”

“That means Tripp must have lied about where he was last night, too.” 

Beckett nods. “And that makes him just as much of a suspect as Simon.” 

 

*end part two*


	3. Part Three

**Summary for the Chapter:**

> "I think our victim figured out something she shouldn’t have and was killed for it. And these notes," Castle says pointing to the photograph, "are the clues she used to come to that conclusion. All I need to do is figure out what they say."

**Notes for the Chapter:**

> Several months ago, reema-patel won safeword_apples’s Mini-Hiatus Pop Quiz contest, the spoils of which was a 500 word fic from me based on a prompt of her choosing. The prompt she gave me was: _pillow fight_ , which it turns out was a pretty awesome prompt because my little 500 word vignette has since turned into a full-on case file. Oops? In any case, I thank her for her patience; this story has been far too long in coming. 
> 
> Research information cited in this story is taken from the [National Alzheimer’s Association Research Center](http://www.alz.org/research/overview.asp) and [Science Daily](http://www.sciencedaily.com/releases/2011/12/111209105746.htm).
> 
> Thanks goes as always to my own personal adverb protection officer gabolange and to girlunravelled who helped nurse me through the daunting plot-writing process.

“Uh-oh.”

Castle looks up from the blown-up photograph of Claudia’s note-covered computer monitor to find his daughter eyeing him warily from the loft’s front door. “’Uh-oh’ what?”

“You’re home early.”

“So?”

“That usually means you’ve done something stupid and Beckett’s sent you home.”

“I’ll have you know,” he starts indignantly, then pauses to consider her observation. “Okay, fair enough. But _this_ time is different. Beckett has seen fit to give me an assignment.”

“Really?” Dropping her purse and coat at the foot of the stairs, Alexis crosses the room and settles herself beside him on the couch. “No stealing or underhanded ploys this time?” she asks, doing a double-take as she leans in to get a better look at what he’s been studying. “Is that my statistics textbook?”

“Yes,” Castle replies firmly. “Turns out I should have paid more attention in Old Fitz’s freshman research class.” 

“Why?”

“I think our victim figured out something she shouldn’t have and was killed for it. And these notes,” he says pointing to a hard copy of the photo he'd snapped of Claudia's computer, “are the clues she used to come to that conclusion. All I need to do is figure out what they say.” 

Picking up the image, Alexis squints as she reads the scribble on each of the notes in turn. “So it’s kind of like piecing together the clues on Beckett’s murder board.” 

“If she were writing the whole thing in some kind of freaky alien language, yes.” 

“Just because you can’t read it doesn’t mean no one else can.” 

Castle stills, then abruptly jumps up from the couch and heads for the kitchen.

“Dad?” Alexis watches in confusion as he reaches into his pants pocket with one hand while rummaging through a one of the kitchen drawers with the other. “What are you doing?”

“Looking for my phone. And these,” he proclaims triumphantly, raising a pair of kitchen shears into the air.

Keying in a number, Castle tucks the phone against his ear and breezes over to collect the photograph and drop a kiss on his daughter’s furrowed brow. “Thank you,” he mouths silently, then raises his voice as the person on the other end of the line picks up. “Oh good; you’re still there.”

* * * *

“This had better be good, Castle.”

The man in question stop short in the morgue’s doorway. “How’d you know it was me?”

Lanie makes a show of checking her watch. “Because it’s eight-thirty at night and after the kind of day I’ve had no one else would be stupid enough to stand between me, my fuzzy slippers and ‘The Bachelor’.”

“You watch ‘The Bachelor’?”

Lanie turns to fix Castle with a steely glare.

“Right; not the point.” Castle pulls an envelope out of his jacket pocket. Opening the flap, he dumps its contents onto the nearby autopsy table. 

“And _this_ is?” she asks, watching dubiously as Castle spreads the pile of roughly cut pieces of photograph across the stainless steel. 

“These notes meant something to Claudia Santos – and her killer. At first, I assumed the notes all fit together, like pieces of a puzzle. But then I realized: the easiest way to hide something you don’t want anyone else to see is in plain sight.” Castle gestures to the pile on the table. “Somewhere in all of this is the one note that holds the answer to why Claudia Santos was killed.”

“And so rather than figure the rest out for yourself, you decided to come down here and get me to do your work for you?” Off his startled look, she explains, “That’s right; Beckett was here earlier and told me all about this little assignment of yours. In case you were wondering, I told her she was crazy.”

“I wasn’t. But thanks for the vote of confidence.”

“Now that’s odd.” Lanie nudges Castle aside and lifts picks up one of the cut outs for a better look.

“What?”

“These notations. It looks like a standard coding reference for individual points of data.”

“Okay. And that means what exactly?” 

“For a study as large as Tripp’s, each individual sample or subject is assigned a coded number for identification. It looks like Claudia was giving these particular samples a second look. And before you get all excited, there are plenty of legitimate, purely scientific reasons why Claudia might have been interested in these particular entries.”

“Legitimate doesn’t mean it couldn’t have also gotten her killed.” 

“You’d need to have a look at the data to know for sure,” she says, collecting the cutouts and handing them to him. 

Castle grins and slips the photos into his pocket. “I can do that. Well, the guys in IT can do that. Thanks, Lanie. I owe you.”

“And don’t you think for a second I’ll let you forget it,” she calls after him as he strides out of the autopsy bay.

* * * * 

When Castle arrives at the precinct the next morning, coffees in hand, Beckett is already at her desk with her phone pressed to her ear. He’s encouraged to see that she’s taking notes as she listens, and as he sets her cup on the desk before her, he takes the opportunity to sneak a peak. 

By the time she hangs up the phone, he’s in his chair, grinning smugly in between sips. “Admit it: you owe me a burger.”

“Don’t you mean I owe _Lanie_ a burger?” she counters with a pointed arch of her eyebrow.

“I was making use of the resources I had available to me. A little trick I learned from one of the best.” 

Beckett leans back in her chair and gives him a once over. “I never did buy into that adage about old dogs.”

“I’m not even going to dignify that with a response.” 

Grinning, Beckett reaches for the steno notebook on her desk. “The guys in IT took a look at the files for the samples on Claudia’s list. Each sample is saved as its own file, then entered into a spreadsheet for analysis. Every file has an internal timestamp indicating when it was loaded into the spreadsheet. The files on Claudia’s list? Were all entered at the same time.”

“That doesn’t sound particularly scribble-worthy,” he point out, waving a hand at the notebook in her hand.

Beckett grins. “No. But the fact that they were re-entered – with different values – almost a month later certainly is.”

“Someone altered the data.” Castle quirks his lips. “And given the level of Tripp’s excitement yesterday, I’m going to hazard a guess and say it was for the better?” 

Beckett nods and hands Castle the notepad. “All of the alterations were traced back to the same workstation in the lab.” She watches him read, waiting for the telltale smile to form on his lips before adding, “I told Ryan and Esposito to bring him in.”

Castle grins. “But did you say ‘Simon says’?” 

* * * *

“Why would I _do_ something like that?”

“You tell me,” Beckett says, her face an impassable mask as she stares at Simon from across the interrogation room table. 

He doesn’t answer the question, but the slight sheen of sweat across his brow is telling enough.

“The evidence clearly shows that the data was altered from _your_ password-protected workstation.”

“Sometimes I forget to log off. Anyone with access to the lab could have used that workstation.”

Beckett continues her explanation as if he hasn’t spoken. “Changes that Claudia inadvertently discovered. And when you realized that she was on to you, you decided to take whatever means necessary to protect yourself and ensure the success of the project.” 

“What? No!”

“C’mon Simon,” Castle says, his hard gaze at odds with the ease of his tone, “Being co-author of what could potentially be one of the most groundbreaking studies in Alzheimer’s research would open a lot of doors professionally – unless, of course, Claudia told the Institutional Review Board that the study was actually a failure.”

“There’s no such thing as a failed research study, Mr. Castle. Some of our most important scientific breakthroughs have come from so-called ‘failed’ research studies.”

“The point remains: your professional future would have been a hell of a lot rosier if you’d had a part in Dr. Tripp’s miraculous discovery.”

“Maybe. But part of the scientific discovery process is independent verification of results. Any falsification would eventually be discovered and in a couple years my career – along with anyone else associated with the project – would _really_ would be over.” 

“That still doesn’t explain why you lied to us about where you were the night Claudia was killed.”

“I didn’t lie. I was at the lab.”

Beckett cocks her head. “Then why does the keycard entry system for the Gamma Alpha Lambda house have you entering the building at seven-thirty?” 

“Okay, yes; I was there. But I left a few minutes before the lock-in was supposed to start.”

“I thought you didn’t go for the undergraduate party scene?” Beckett asks.

“I don’t.”

Castle narrows his eyes. “But you do go for a particular undergraduate party girl, right?”

“Claudia isn’t—” Simon licks his lips and swallows, “—wasn’t like that. She liked to have fun, sure. But when push came to shove, academics always came first. It’s one of the reasons I fell in love with her.”

“And you didn’t tell us this yesterday because…?”

“Claudia wanted to keep things quiet. Dr. Tripp doesn’t approve of relationships inside the lab; he thinks they distract from the work. But he’s wrong; being together made both of us _better_.”

“Better how?”

Simon takes a moment to consider the question. “It’s different, having someone who understands and shares the passion you have for what you do. It matters more. _They_ matter more.”

“And in all those hours spent together both in and outside the lab, she never once mentioned to you that she suspected someone had been altering the study data?”

“I wish she had. Maybe then…” Simon drops his gaze and shakes his head. “I was going to propose to her next month, after graduation. The ring is sitting in my sock drawer at home.” He pauses, and when he looks up his expression is resolute. “I didn’t know. And I sure as hell didn’t kill her.” 

* * * *

“He’s telling the truth.” Ryan rotates his computer monitor so the rest of them can see the grainy image of Simon walking out the front door of the Gamma house. “Timestamp is just before nine o’clock. We didn’t catch it the first time around because we were focusing on footage from later that night.” 

Esposito frowns. “So Simon isn’t our guy.” 

“And we’re back to square one,” Beckett adds with a sigh.

“Not necessarily.” Castle turns and points to the photos of Claudia’s Post-It Notes on the murder board. “We have our motive: Claudia’s discovery of the altered data. Figure out who altered the data, and you’ve got your killer.”

Beckett crosses her arms and makes her way over to the murder board. “There are at least twenty people with access to that lab.” 

“But how many of them would have been ready, willing and able to commit the equivalent of professional suicide?” Castle asks as he moves to stand beside her.

Ryan joins them a moment later. “What do you mean?”

“Simon said it himself,” Castle explains. “Any alterations to the data would have eventually been discovered when other research groups tried to replicate the results.”

Esposito is the last to come around the desk. “So?” 

“So,” Castle drawls, “anyone else working in that lab would know that, too.”

“You think we should be looking for someone outside the lab?” Ryan asks dubiously.

Beckett shakes her head. “We didn’t find any sign of a break-in. Besides, why would someone not involved in the project want to improve the results? If anything, I’d expect someone breaking in to want to sabotage the study, not help it along.”

“Which means we’re looking for someone on the project, with access to the lab, who doesn’t care about what happens to their career a couple of years down the line?” Esposito frowns. “No way. Every one of the people working on that project was either a student or a post-grad.”

“Not everyone,” Castle says, casting a meaningful glance at Beckett.

Beckett acknowledges the point with a grim smile. “Ryan?”

“On it,” he replies, already reaching for the phone. 

 

*end part three*


	4. Part Four

**Summary for the Chapter:**

> Together Castle and Beckett step into the interrogation room, where their suspect is already waiting for them.

**Notes for the Chapter:**

> Several months ago, reema-patel won safeword_apples’s Mini-Hiatus Pop Quiz contest, the spoils of which was a 500 word fic from me based on a prompt of her choosing. The prompt she gave me was: _pillow fight_ , which it turns out was a pretty awesome prompt because my little 500 word vignette has since turned into a full-on case file. Oops? In any case, I thank her for her patience; this story has been far too long in coming. 
> 
> Research information cited in this story is taken from the [National Alzheimer’s Association Research Center](http://www.alz.org/research/overview.asp) and [Science Daily](http://www.sciencedaily.com/releases/2011/12/111209105746.htm).
> 
> Thanks goes as always to my own personal adverb protection officer gabolange and to girlunravelled who helped nurse me through the daunting plot-writing process.

Together Castle and Beckett step into the interrogation room, where their suspect is already waiting for them. He looks up as they enter and is almost immediately wracked with a fit of coughing that lasts well after they’ve both taken their seats. 

“That’s quite a nasty cold,” Castle comments as their suspect dabs at his mouth with a handkerchief.

“Except it isn’t a cold, is it, Dr. Tripp?” Beckett asserts. “It’s something far more serious than that.”

Tripp holds Beckett’s gaze for a moment, then reaches across the table to show her the blood-stained cloth in his hand. “Stage four lung cancer, with metastases to the pelvic bone and lymph nodes. My prognosis is less than six months.”

“I’m sorry to hear that.”

“So was I,” Tripp says with a self-deprecating laugh. “I’ve seen so many advances in medicine during my lifetime; you’d think we’d have been able to come up with something—” he stops short, swallowing hard. “The oncologist wanted to start me on chemotherapy and radiation treatments to slow the tumor’s progression. But I know better than most what that kind of thing does to a body: the constant sickness, the fatigue. By forgoing treatment, I assumed I would feel well enough to be able to keep working and complete my research before nature took its course.”

“One last, shining moment of achievement before the end,” Castle says. “Except your research wasn’t going anywhere, was it? Not without help.”

Tripp doesn’t bother to pretend that he doesn’t know what Castle is talking about. “I never married, have no children; this discovery was to have been my only legacy, something that would live on long after I was gone, like Salk’s vaccine or Rotengen’s X-ray. When I saw the preliminary analyses and realized what was happening…it was only a week or so after my diagnosis. I know that’s no excuse but under the circumstances, I didn’t know what else to do.”

“You lost your life and your life’s work, all in the span of a few days.”

Tripp nods. “It was too much. So I took advantage Simon’s carelessness and used his workstation to alter the data. I simply assumed that, by the time the scientific community had done its due diligence and realized what I’d done, it wouldn’t matter anymore.” 

“I think people like Claudia and her grandmother would beg to differ.” 

Tripp’s lips curl into a faint, melancholy smile. “That’s precisely what she said to me.” 

“Right before you killed her.”

Tripp’s pallor takes on a sickly hue at the steel in Beckett’s tone. “I am not a violent person, Detective Beckett.”

“The evidence says otherwise, professor.” 

Swallowing thickly, Tripp stares down at his tightly folded hands in his lap. When he looks up a few seconds later, his eyes are over bright with tears. “As soon as I realized that she’d discovered what I’d done, I went to the sorority house to talk to her. I wanted to explain why I’d done it, and try convince her not to report what she’d found. That was all.”

“Except Claudia wouldn’t listen.”

“She said it wasn’t right, to give people false hope, that I’d become blinded by my own ego and lost sight of the true purpose of our research. She insisted on going to the IRB first thing Monday morning to report what she’d found. Nothing I said could change her mind. The next thing I knew,” Tripp concludes, his voice cracking with emotion, “there was a pillowcase in my hands and it was wound around Claudia’s throat.” Tripp pauses to focus his mournful gaze on her. “As I said: I’m not a violent man. But I’d say the facts more than support the hypothesis, wouldn’t you?”

* * * *

From the break room window, Castle watches as a pair of uniforms escort a handcuffed Dr. Tripp from the interrogation room. “I really hate it when the good guy turns out to be the bad guy.” 

“Desperation can make even a person with the best of intentions do some pretty awful things.” Beckett reaches for the coffee carafe and fills first her mug, then Castle’s. “Besides, I wouldn’t exactly call a man who puts his own ego ahead of his ethical responsibility a ‘good’ person.” 

“He spent his entire life working to find a cure for a terrible disease. Doesn’t he deserve at least some credit for that?”

Beckett follows the two sugars she’s added to his coffee with a splash of cream before handing it to him. “Maybe; but my job isn’t to determine whether a person is inherently ‘good’ or ‘bad’. Like it or not, Jeremy Tripp killed someone. And in the eye of the law, that’s ultimately what matters.” 

“You know,” Castle says as they make their way across the bullpen to Beckett’s desk, “this whole case has got me thinking.”

Beckett shoots him a warning look as she takes her seat. 

“My thoughts have absolutely nothing to do with pillow fights or half-naked co-eds, I swear.” 

“Then by all means, continue.”

“Cogito ergo sum.”

Beckett’s brow furrows. “I think, therefore I am?”

Castle nods. “Except Descartes got it wrong. What he should have said was ‘I _remember_ , therefore I am’.”

“Correcting the Father of Modern Philosophy? Seems a bit lofty even for you.”

“What else are we but the sum of our experiences?”

She frowns, a momentary shadow darkening her features. “I like to think it’s what we learn from them that make the difference.” 

“Would you want to forget?” Castle asks after a beat. “If you had the choice?” 

Beckett shakes her head. “For better or for worse, my mother’s murder is one of the reasons I am who I am. Lose that, and I lose myself.” 

“Can’t have that,” he murmurs, giving her a soft smile. 

Beckett holds his gaze for a moment before busying herself with a stack of files on her desk. “So, any other tenets of philosophy you’d like to rewrite?”

Castle makes a show of thinking it over. “Nope. I’m good. Drink?” he asks, hitching a thumb in the direction of the elevator as he rises to his feet.

“It’s three o’clock in the afternoon.”

“As good a time as any to make a new memory, wouldn’t you say?” 

Beckett glances at the papers and files spread across her desk. “Old Haunt?” 

“Where else?”

“Okay, Castle.” She stands and reaches for her jacket. “Let’s play hookey.”

“I love it when you talk dirty,” he says as he trots across the bullpen after her.

 

*fin.*


End file.
